1. Field of the Invention
The present invention related to an improved roof assembly, particularly of the type utilizing flexible membrane material, preferably single-ply material, as the uppermost waterproofing layer of the roof assembly. More particularly, the present invention is directed to an improved roofing assembly of the type utilizing air sealed decking comprising corrugated (preferably metal) sheets, wood decking, concrete planking composite panels, poured concrete and the like placed on a structural framework with the emphasis that this invention is particularly useful in combination with existing roofing assemblies such as built up roofing assemblies.
2. Prior Art
Supportive decking sheets, having corrugations for reinforcement, have been previously used in roofing systems of the type using built-up roof waterproofing and flexible single-ply membranes. These decking sheets are attached to an underlying roof support structure, such as metal I-beams, purlins, joints, a wood frame, or the like. These decking sheets are air permeable at their joints and serve to support insulation boards on the top thereof, which insulation boards are then covered by a roofing waterproofing membrane preferably by a single-ply membrane. Such roof decking sheets are commercially available. Air permeable wood decking composite decking and concrete plank decking are also readily commercially available through construction material supply outlets.
In order to accommodate the wind uplift forces that occur in use of such roofing assemblies on a building, especially the very high forces on tall buildings and structures adjacent perimeter edges of buildings, it has been known to provide venting valves through roof membrane. See U.S. Pat. Nos. 4,223,486 and 4,557,081; which are assigned to Thomas L. Kelly, all of the contents of which are incorporated herein by reference, for examples of venting valve systems that have been used. It has also been known to provide some type of sealing envelope (e.g., membrane or film) that extends over the top of sheet metal or other air permeable decking which effectively seals the insulation boards in an air-tight envelope when topped by the membrane. Certain areas of the perimeter and protrusions through the roof which is being covered are particularly important to seal.
In prior systems, were the deck joints are caulked and sealed or in monolithic decks like a poured-in-place concrete deck, the deck serves as an air-tight seal. In these systems flashing is provided between the deck seal or monolithic concrete deck and the membrane overlying the insulation to form a sealed air-tight envelope at protrusions penetrations and perimeters.
In all of the prior systems which employ an air barrier or seal placed upon the top of an air permeable decking, the wind uplift forces are transferred to the bottom of the air barrier layer pushing upward from inside the building, through the air permeable deck. The integrity of the roof systems vis-a-vis the wind uplift forces depends upon the integrity of the insulation, the insulation skin, and the fastener or adhesive holding capability to the deck to keep the roof assembly in place.
Typically, a roof assembly would incorporate mechanical fasteners that would penetrate the insulation boards and include an overlying washer-type hold-down on top of the insulation. These fasteners would then be screwed or bolted through the insulation and air barrier sheet and roof assembly into the permeable decking underneath. Under certain wind uplift conditions, the connection between the insulation board fasteners and the decking can fail resulting in the insulation board being pushed against the overlying roof waterproofing membrane to cause a roof failure.
Prior roofing systems did not employ air seal barriers from the interior of the building, for example, at penetrations, and wind forces would then focus the stress of uplift pressures through the roof assembly directly into the waterproofing membrane. These prior systems also required a barrier sheet to be interposed between the top of the decking and the bottom of the insulation board or board layers. This air barrier sheet would also then be penetrated by the fasteners for the hold-down of insulation boards. Under certain circumstances during assembly of such roofs, the air barrier could tear at the location of the hold-down fasteners, thereby diluting the air barrier effect
The sealed roof deck wind vacuum transfers disclosed in Thomas L. Kelly's U.S. Pat. No. 4,888,930, all of the contents of which are incorporated herein by reference, was a great improvement over the prior art previously discussed. However, the system as disclosed in the '930 patent requires careful placing of the roof deck panels for the application of the caulking between and into the roof decking joints. While well suited for its intended purpose, this system can be burdensome, cumbersome and time consuming since each roof deck panel must be laid in place individually and caulked on the interior of the joint prior to laying down of the overlapping panel.
Further improvements were disclosed in Thomas Kelly's disclosure Ser. No. 08/362,226 filed Dec. 23, 1994 which is incorporated herein by reference. Although all of the aforementioned disclosures have led to improvement of sealed roof deck wind vacuum transfer systems, there remains a need for further improvement.
Notwithstanding, the exceptional improvements in wind uplift protection, which improvements have significantly reduced the incidents of roof failure associated with this effect, storm grade winds, particularly those over 100 mph, are quite capable of tearing an entire roof off the building to which it is affixed. The two reasons for this are understandable upon a brief review of the dynamics of wind uplift and thermal expansion and contraction of roof deck and perimeter structures.
The dynamics involved in wind uplifts are created by two fluid streams and a principle of physics known as the Bernoulli principle. The fluid streams at issue are: first, the flow of air across the top of the building and second the upward flow of air caused by a horizontal air flow colliding with the side of the building and being redirected upwards. The two air streams create a horizontal vortex at the windward edge of the building which urges the roofing membrane upward. This, in combination with the Bernoulli principle, which states that as the velocity of a fluid increases, pressure (as well as temperature) decreases, thus providing lift, is a formidable opponent in the struggle to maintain the roof membrane in its desired position. Add to this the instability caused by thermal expansion and contraction of the roof deck and surrounding structures, (as well as structures extending through the roof deck) and it is easy to comprehend first why roofs blow off.
Thermal expansion and contraction of the various structures is concentrated mainly in the longest direction of the structure. For example, a roof deck will expand and contract mostly in the horizontal direction while a building wall and parapet will expand and contract mostly vertically. This discordant movement creates substantial stress on the air sealing compositions and structures (such as nailers) in the precise locations most critical to securing the entire roof structure. Alternately stated, the described movement loosens nailers and fasteners in the perimeter or penetration areas most susceptible to wind uplift forces. Moreover, once these fastening structures have been defeated there is little to prevent the entirety of the roof from blowing off. As stated above, it is not difficult to comprehend why roofs blow off.
Heretofore, no reasonable or effective method or apparatus has been suggested to alleviate this obviously vexatious situation.